An implantable cardiac stimulus device is shown in FIG. 1. The device 10 includes a canister 12 that houses electronics for controlling electrical cardiac stimulation. An electrode 14 may optionally be placed on the canister 12, and a lead 16 extends from the canister 12 and carries one or more lead electrodes 18, 20. The device may be suited for delivery of cardiac stimulus as a pacing device providing low energy pulses timed to help regularize cardiac function, or may be suited instead for delivery of higher energy pulses to convert a malignant cardiac event to normal sinus rhythm. When properly implanted and properly functioning, impedances between pairs of electrodes 14, 18, 20 will generally fall within a known range. When the measured impedance falls outside the known range, it can often be determined that something is wrong and, possibly, that the device should be explanted and replaced. The device 10 may include telemetry circuitry/devices allowing it to communicate from an implanted position with an associated programmer. Such communication may include annunciation of a lead impedance measurement that is outside of an expected range. The impedance may fall out of range for any number of reasons, for example, device failure, improper lead position, or anatomical abnormality. Lead impedance measurement is therefore a desirable function of such implantable medical devices.